Magnetoresistive magnetic sensor with tunnel effect and magnetic storage apparatus

ABSTRACT

A magnetoresistive head has a high low resistance and a high MR ratio at room temperature and a S/N ratio that does not decrease sharply upon application of a bias voltage. The magnetoresistive head includes a soft magnetic free layer, a non-magnetic insulating layer, and a ferromagnetic pinned layer. The ferromagnetic pinned layer may have a spin valve layer whose magnetization is fixed with respect to the magnetic field to be detected. The magnetization of the soft magnetic free layer is permitted to rotate in response to an external magnetic field, thereby changing the relative angle with the magnetization of the ferromagnetic pinned layer and producing a magnetoresistive effect whose absolute value has a peak at a temperature range of 0-60° C. with a bias voltage Vs (applied across the ferromagnetic pinned layer and the soft magnetic free layer) in ranges of +0.2 to +0.8 V and −0.8 to −0.2 V.

PRIORITY TO FOREIGN APPLICATIONS

This application claims priority to Japanese Patent Application No.P2001-013958.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an information recording-reproducingapparatus and a magnetic recording-reproducing head to be mountedthereon, and, more specifically, the present invention relates to aninformation recording medium that retains information by means ofinverted magnetic domains on a magnetic recording film formed on asubstrate and an information reproducing apparatus designed to reproduceinformation by detecting leakage magnetic fluxes from the recordingmedium.

2. Description of the Background

In recent years, magnetic disk apparatuses have greatly increased inrecording density, with the track size for recording bits becomingsmaller and smaller. These smaller domains require the magneticreproducing head to have a higher sensitivity than past devices. Onesuch reproducing head is reported in “Nikkei Electronics” No. 774, Jul.17, 2000, pp. 177-184. The device disclosed in this reference employs atunnel magnetoresistive film as a next-generation super-sensitivemagnetic sensor.

This first conventional example is characterized by a patterned laminatestructure consisting of a lower magnetic shield layer, an electrodelayer, a soft magnetic free layer, a non-magnetic insulating layer, aferromagnetic pinned layer, an antiferromagnetic layer to fix thedirection of magnetization of the ferromagnetic pinned layer, and anelectrode layer. The laminate film has, at both ends thereof, a hardmagnetic layer to stabilize the direction of magnetization of thenon-magnetic free layer and also has an insulating film to insulate theupper and lower magnetic shields.

In the above-mentioned example, the soft magnetic free layer is formedfrom a CoFe alloy; the non-magnetic insulating film is formed fromaluminum oxide; and the ferromagnetic pinned layer is formed from a CoFealloy. The sensor film has a very low resistance and a very high MRratio (calculated by dividing the maximum resistance change due toapplied magnetic field by the initial resistance) at room temperature.For instance, a sensor film having a resistance per area of 33.5 Ω·μm²has an MR ratio of 31.6%. A sensor film having a resistance per area of14.2 Ω·μm² has an MR ratio of 24.4%. A sensor film having a resistanceper area of 5.6 Ω·μm² has an MR ratio of 12.3%.

A second known example of sensor film is disclosed in Physical ReviewLetters, Vol. 82, No. 21, pp. 4288-4291. This sensor film employs alaminate film consisting of CoFe alloy, SrTiO₃, andLa_(0.7)Sr_(0.3)MnO₃. It gives a high MR ratio (50% maximum) with a biasvoltage (Vs) of −0.4 V at 4.2K.

A third known example of sensor film is disclosed in Physical ReviewLetters, Vol. 82, No. 3, pp. 616-619. This sensor film employs alaminate film consisting of Ni_(0.8)Fe_(0.2), Ta₂O₅, Al₂O₃, andNi_(0.8)Fe_(0.2). It gives an MR ratio of 4% with a bias voltage (Vs) of−0.2 V at room temperature.

The above-mentioned known examples may be characterized by one or moreof the following disadvantages. First, with respect to a sensor filmhaving a low resistance and a high MR ratio at room temperature, such atunnel magnetoresistive sensor in the form of CoFe/Al oxide/CoFelaminate film may include an MR ratio which steeply decreases (as shownin FIG. 11) when a bias voltage is applied across the two CoFe layers. Abias voltage (Vh) of approximately 0.4 V may decrease the MR ratio by upto half from that without bias voltage. When applied to a magnetic readhead, this sensor film may have a decreased output in proportion to thebias voltage, unlike the known giant magnetoresistive magnetic read inpractical use. Additionally, the tunnel magnetoresistive head, unlikethe conventional giant magnetoresistive magnetic read head, may have adecreased signal-to-noise ratio because of its inherent shot noiseproportional to the bias voltage.

In order to address one or more of these potential problems and torealize a practical tunnel magnetoresistive head suitable for magneticrecording-reproducing apparatuses with very high recording density, itis preferred to reduce the head resistance. Toward this end, it may bepreferable to reduce the thickness of the aluminum oxide film used asthe non-magnetic insulating film.

The second known example preferably only needs to meet less stringentrequirements for head resistance than the conventional head of the firstknown example because the MR ratio, which is measured at 5K, reaches themaximum in the vicinity of the head-operating voltage (Vs=−0.5 V).However, a problem may ensure because La_(0.7)Sr_(0.3)MnO₃ is asubstance which undergoes phase transition from ferromagnetic materialto paramagnetic material in the neighborhood of room temperature. Inother words, its MR ratio becomes almost zero at 0-60° C. (which is theoperating temperature of the magnetic recording apparatus).

In the case of the third known example, the MR ratio reaches a maximumin the vicinity of the head-operating voltage (Vs=−0.2 V). This MRratio, however, is smaller than that of the giant magnetoresistive headin practical use at the present. Therefore, the third known example maynot be suitable for future magnetic recording-reproducing apparatuseswith very high recording densities.

SUMMARY OF THE INVENTION

At least one embodiment of the present invention is directed to amagnetic sensor which preferably comprises a soft magnetic layer and aferromagnetic layer, with a non-magnetic layer interposed between themsuch that the magnetization of said ferromagnetic layer is fixed withrespect to the magnetic field to be detected. The invention may alsoinclude a magnetoresistive film that changes in magnetoresistanceaccordingly as the magnetization of the soft magnetic layer rotates inresponse to the external magnetic field, thereby changing the relativeangle with the magnetization of the ferromagnetic layer. Themagnetoresistive film may show a change in magnetoresistance upon theapplication of a detecting current across the soft magnetic layer andthe ferromagnetic layer through the non-magnetic layer, with the ratioof change (in absolute value) in magnetoresistance of themagnetoresistive film having a maximum value greater than 20% at atemperature in the range from 0° C. to 60° C. and with a bias voltage(Vs) applied across the ferromagnetic layer and the soft magnetic layerbeing in the range from +0.2 to +0.8 V and from −0.8 to −0.2 V.

The present invention is also preferably directed to a magnetic sensorof tunnel junction laminate structure comprising a soft magnetic freelayer, a non-magnetic insulating layer, and a ferromagnetic pinnedlayer, wherein the ferromagnetic pinned layer has a spin valve layerwhose magnetization is fixed with respect to the magnetic field to bedetected. The soft magnetic free layer may permit its magnetization torotate in response to the external magnetic field, thereby changing therelative angle with the magnetization of the ferromagnetic pinned layerand producing the magnetoresistive effect, with the absolute value ofthe magnetoresistive effect having a peak at a temperature in the rangefrom 0° C. to 60° C. and for a bias voltage Vs (applied across theferromagnetic pinned layer and the soft magnetic free layer) in therange from +0.2 to +0.8 V and from −0.8 to −0.2 V.

In the tunnel magnetoresistive magnetic sensor, the ferromagnetic pinnedlayer may be formed from Fe₃O₄ or at least one oxide or compound of Crand Mn. Additionally, in the tunnel magnetoresistive magnetic sensor,the nonmagnetic insulating layer may be formed from at least one oxideof Sr, Ti, and Ta. Moreover, in the tunnel magnetoresistive magneticsensor, the soft magnetic free layer may be a layer of Co/Fe alloyformed on the nonmagnetic insulating layer or a laminate layerconsisting of a layer of Co/Fe alloy and a layer of Ni/Fe alloysequentially formed on the non-magnetic insulating layer.

Alternatively, in the tunnel magnetoresistive magnetic sensor, the softmagnetic free layer may be a layer of Co/Fe alloy whose Co content is inthe range from 70 atom % to 100 atom %, and the ferromagnetic pinnedlayer may be a layer of Co/Fe alloy whose Co content is in the rangefrom 0% to 70%. Furthermore, the non-magnetic insulating layer may beformed from at least one oxide of Sr, Ti, and Ta.

In the tunnel magnetoresistive magnetic sensor, a layer of Ni/Fe alloymay also be laminated onto that side of the soft magnetic free layer ofCo/Fe alloy which is opposite to the non-magnetic insulating layer.Alternatively, a second non-magnetic insulating layer and a secondferromagnetic layer may be sequentially laminated onto that side of theferromagnetic pinned layer which is opposite to the non-magneticinsulating layer. The second ferromagnetic layer may be formed fromFe₃O₄ or at least one oxide or compound of Co, Cr, and Mn.

Further, in the tunnel magnetoresistive magnetic sensor, thenon-magnetic insulating layer may be formed from at least one oxide orcompound of Sr, Ti, Ta, and Al. The soft magnetic free layer may be alayer of Co/Fe alloy formed on the non-magnetic insulating layer or alaminate layer consisting of a layer of Co/Fe alloy and a layer of Ni/Fealloy sequentially formed on the nonmagnetic insulating layer.

Additionally, the tunnel magnetoresistive magnetic sensor of the presentinvention preferably provides electrodes electrically connectedrespectively to the soft magnetic free layer, the ferromagnetic pinnedlayer, and the second ferromagnetic layer, so that current flows fromthe second ferromagnetic layer to the ferromagnetic pinned layer.

The present invention is also directed to a magnetic head whichcomprises any of the above magnetic sensors with a magnetic shield onits upper and lower parts and a metal layer placed between the magneticsensor and the magnetic shield so as to electrically connect themagnetic sensor and the magnetic shield together.

The present invention is also directed to a recording-reproducingmagnetic head which comprises the above magnetic head and aninduction-type thin film magnetic head formed thereon. Theinduction-type thin film magnetic head preferably comprises: a lowermagnetic core, an upper magnetic core, and a non-magnetic layerinterposed between the lower and upper cores. The upper magnetic coremay be connected at its forward end to the lower magnetic core with amagnetic gap interposed between them. The upper magnetic core may alsobe connected at its rear end directly to the lower magnetic core througha back-contact formed from a magnetic material.

The present invention is also directed to a magneticrecording-reproducing apparatus which preferably comprises a magneticrecording medium and said magnetic sensor or magnetic head, the formerretaining information by means of inverted magnetic domains formed onthe surface thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

For the present invention to be clearly understood and readilypracticed, the present invention will be described in conjunction withthe following figures, wherein like reference characters designate thesame or similar elements, which figures are incorporated into andconstitute a part of the specification, wherein:

FIG. 1 is a perspective view (1A) and a sectional view (1B) showing atunnel effect-type magnetic read head according to an embodiment of thepresent invention;

FIG. 2 shows a diagram of the dependence on bias voltage of the MR ratioof a tunnel effect-type magnetic read head according to an embodiment ofthe present invention (2A) and a diagram defining the direction ofapplication of bias voltage (2B);

FIG. 3 is a diagram showing the dependence on bias voltage of the MRratio of the tunnel effect-type magnetic read head according to anembodiment of the present invention;

FIG. 4 is a perspective view (4A) and a sectional view (4B) showing atunnel effect-type magnetic read head according to an embodiment of thepresent invention;

FIG. 5 is a perspective view (5A) and a sectional view (5B) showing thetunnel effect-type magnetic read head according to an embodiment of thepresent invention;

FIG. 6 is a diagram showing the dependence on bias voltage of the MRratio of the tunnel effect-type magnetic read head according to anembodiment of the present invention;

FIG. 7 is a sectional view showing a magnetic recording-reproducing headwhich consists of the tunnel effect-type magnetic read head of thepresent invention and an induction-type magnetic recording head;

FIG. 8 is a sectional view showing a magnetic recording-reproducing headwhich consists of the tunnel effect-type magnetic read head of thepresent invention and a single-magnetic pole magnetic recording head;

FIG. 9 is a diagram showing a magnetic recording-reproducing apparatuswhich is equipped with any of the magnetic read heads according to thepresent invention and the magnetic recording-reproducing head shown inFIG. 7 or FIG. 8;

FIG. 10 is a diagram showing the relation between the bias voltage andthe signal-to-noise ratio of a tunnel magnetoresistive read headaccording to the present invention; and

FIG. 11 is a diagram showing the dependence on bias voltage of the MRratio of the conventional tunnel effect-type magnetic read head.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the figures and descriptions of the presentinvention have been simplified to illustrate elements that are relevantfor a clear understanding of the present invention, while eliminating,for purposes of clarity, other elements that may be well known. Those ofordinary skill in the art will recognize that other elements aredesirable and/or required in order to implement the present invention.However, because such elements are well known in the art, and becausethey do not facilitate a better understanding of the present invention,a discussion of such elements is not provided herein. The detaileddescription will be provided hereinbelow with reference to the attacheddrawings.

FIG. 1 shows a tunnel effect-type magnetic sensor and a magnetic readhead provided therewith in one exemplary embodiment of the presentinvention. FIG. 1A is a perspective view showing the tunnel effect-typemagnetic sensor and a magnetic read head provided therewith. FIG. 1B isa sectional view showing the tunnel effect-type magnetic sensor and amagnetic read head provided therewith.

There is shown a substrate 101. On the substrate 101 are preferablysequentially formed: a lower magnetic shield 102; a metal layer 103 ofCu, Ta, or Ru; an antiferromagnetic layer 104; a ferromagnetic pinnedlayer 105; a non-magnetic insulating layer 106; and a soft magnetic freelayer 107 with its top being connected to an upper magnetic shield 110through a metal layer 108 of Cu, Ta, or Ru. The magnetic sensor, whichcomprises the soft magnetic free layer 107, the non-magnetic insulatinglayer 106, and the ferromagnetic pinned layer 105, has a front sidewhich is connected to a flux guide 109 of soft magnetic material so thatthe leakage flux from the magnetic recording medium (not shown) isefficiently introduced into the magnetic sensor 112.

In addition, the tunnel effect-type magnetic head is constructed suchthat the laminate film consisting of layers 103 through 108 issurrounded by an insulating layer 111 for electrical insulation becausecurrent has to flow from the lower magnetic shield 102 to the uppermagnetic shield 110 only through the magnetic sensor 112. The lowermagnetic shield 102 and the upper magnetic shield 110 are connectedrespectively to electrodes 114 and 113 for voltage application.

The ferromagnetic pinned layer 105 and the soft magnetic free layer 107are magnetized (in the absence of a magnetic field from the magneticrecording medium) such that their directions of magnetization (withintheir plane) mutually cross at approximately right angles. When amagnetic field (H) is applied from the magnetic recording medium to thesoft magnetic free layer 107 through the flux guide 109, the directionof magnetization within the plane of the soft magnetic free layer 107rotates and the tunnel magnetic resistance between the soft magneticfree layer 107 and the ferromagnetic pinned layer 105 changes inproportion to the angle of rotation.

A detailed description will now be made of exemplary material anddimensions of each layer. The antiferromagnetic layer 104 is composed ofZnO (10 nm thick) for orientation control, NiO (20 nm thick), and α-F₂O₃(2 nm thick), which are sequentially laminated. The ferromagnetic pinnedlayer 105 is formed from Fe₃O₄ (10 nm thick) which is a half-metalmagnetic material having a Curie temperature much higher than roomtemperature. The non-magnetic insulating layer 100 is formed from SrTiO₃(1 nm thick).

The magnetic free layer 107 is a laminate composed of layers of CoFe (1nm thick) and NiFe (3 nm thick). The CoFe alloy is not specificallyrestricted in composition; in this embodiment it is composed of Co (90atom %) and Fe (10 atom %) for appropriate soft magnetic properties.Likewise, the NiFe alloy is not specifically restricted in composition;in this embodiment it is composed of Ni (81 atom %) and Fe (19 atom %).This composition is called permalloy composition.

The metal layers 103 and 108 are preferably 3 nm thick and 10 nm thick,respectively, so that the soft magnetic free layer 107 is positioned atthe approximate midpoint between the lower magnetic shield 102 and theupper magnetic shield 110. Thus, the distance between the lower magneticshield 102 and the upper magnetic shield 110 is approximately 60 nm,which provides a linear resolution sufficient for a magnetic recordingapparatus for very high recording density (0.155 GB/mm² or 100 GB/inch²)

The element comprised of the layers between the lower electrode 103 tothe upper electrode 108 measures approximately 0.3 by 0.3 μm. Theforward end of the flux guide 109 measures approximately 0.15 μm wide,10 nm thick, and 50 nm long. Since the width of the forward end of theflux guide 109 determines the resolution (in the track direction) of themagnetic recording apparatus, the above-mentioned size is small enoughfor a magnetic recording apparatus for very high recording density(0.155 GB/mm² or 100 GB/inch²)

FIG. 2A shows how the MR ratio of the tunnel effect-typemagnetoresistive head constructed as shown in FIG. 1 depends on the biasvoltage (Vs) at room temperature (25° C.). The MR ratio is a ratio ofthe change in magnetic resistance which is defined as the maximum changein resistance due to an applied magnetic field divided by the initialresistance. FIG. 2B defines the direction in which the bias voltage isapplied. In the present invention, the bias voltage is defined withreference to the ferromagnetic pinned layer where Vs=0 V.

It can be noted from FIG. 2A that the MR ratio reaches a maximum when Vsis −0.5 V and decreases rapidly as Vs approaches 0 V. The maximum valueof the MR ratio is approximately 80%, and this value is greater than themaximum value ever conventionally observed. The dependence of MR ratioon bias voltage hardly varies in the temperature range from 0° C. to 60°C. at which the magnetic recording apparatus is used. When the appliedmagnetic field is zero, the electric resistance between the electrodes113 and 114 is approximately 150 Ω, which is adequate for the magneticread head.

Other materials which can be used for the ferromagnetic pinned layerinclude CrO₂ and CuMnAl₂. In the case where CrO₂ is used, theabove-mentioned orientation-controlling film is preferably made of TiO₂and the antiferromagnetic film is preferably made of NiO. In the casewhere CuMnAl₂ is used, the orientation-controlling film is notnecessary. In this case, the lower electrode layer 103 is preferablyformed from Ta and the antiferromagnetic film is formed from PtMn alloy.Other materials for the non-magnetic insulating layer 106 include Ta₂O₅and MgO.

An second exemplary embodiment of the present invention describes a casein which both the soft magnetic free layer 107 and the ferromagneticpinned layer 105 are based on a CoFe alloy. In this case, the lowerelectrode layer 103 is preferably a 12-nm thick Ta film, and theantiferromagnetic layer 104 is a 12-nm thick PtMn film. Theferromagnetic pinned layer 105 is a 3-nm thick CoFe film (containing 50atom % of Co). The nonmagnetic insulating layer 106 is a 1-nm thickSrTiO₃ film.

In this embodiment, the soft magnetic free layer 107 is preferably alaminate composed of a 1-nm thick CoFe film and a 3-nm thick NiFe film.The CoFe alloy is comprised of 90 atom % of Co and 10 atom % of Fe. TheNiFe alloy is not specifically restricted in composition; in thisembodiment it is composed of 81 atom % of Ni and 19 atom % of Fe. Thiscomposition is called the permalloy composition. The metal layer is madeof Ru, and it is approximately 28 nm thick so that the soft magneticfree layer 107 is positioned at a mid-point between the lower magneticshield 102 and the upper magnetic shield 110.

The element comprised of the layers between the lower electrode 103 tothe upper electrode 108 measures approximately 0.3 by 0.3 μm, as in thefirst embodiment.

FIG. 3A shows the dependence of the MR ratio of the tunnel effect-typemagnetoresistive head in this embodiment on the bias voltage Vs at roomtemperature (25° C.). It can be noted from FIG. 3A that the MR ratioreaches a maximum when Vs is −0.5 V and decreases steeply as Vsapproaches 0 V. The maximum value of the MR ratio is approximately 30%.The dependence of the MR ratio on the bias voltage does notsubstantially vary in the temperature range from 0° C. to 60° C. atwhich the magnetic recording apparatus is used. When the magnetic fieldapplied is zero, the electric resistance between the electrodes 113 and114 is approximately 100 Ω, which is adequate for the magnetic readhead.

In the embodiment mentioned above, the CoFe alloy for the soft magneticfree layer 107 contains 90 atom % of Co, and the CoFe alloy for theferromagnetic pinned layer 105 contains 50 atom % of Co. However, it maybe desirable that the CoFe alloy for the soft magnetic free layer 107contain 70-100 atom % of Co and the CoFe alloy for the ferromagneticpinned layer 105 to contain 0-70 atom % of Co.

FIG. 3B shows the dependence of the MR ratio of the tunnel effect-typemagnetoresistive head on the bias voltage Vs at room temperature (25°C.) in the case where the soft magnetic free layer 107 is made of a CoFealloy containing 90 atom % of Co and the ferromagnetic pinned layer 105is made of a CoFe alloy containing 30 atom % of Co. It can be noted fromFIG. 3B that the MR ratio reaches a maximum when Vs is −0.3 V anddecreases steeply as Vs approaches 0 V. The maximum value of the MRratio is approximately 45%. The dependence of the MR ratio on the biasvoltage does not substantially vary in the temperature range from 0° C.to 60° C. at which the magnetic recording apparatus is used. When theapplied magnetic field is zero, the electric resistance between theelectrodes 113 and 114 is approximately 70 Ω, which is adequate for themagnetic read head.

Other materials for the non-magnetic insulating layer 106 may includeTa₂O₅ and MgO as in the first embodiment.

FIG. 4 shows a third exemplary embodiment of the present invention inwhich the tunnel effect-type magnetoresistive head shown in FIG. 1 ismodified such that the element comprised of the layers between the lowerelectrode 103 and the upper electrode 108 is exposed toward that side ofthe head which faces the recording medium. In this case, the materialsand dimensions of each layer are preferably identical with those in thefirst exemplary embodiment. However, the output of the magnetic readhead increases because the magnetic flux does not attenuate in the fluxguide.

FIG. 5 shows a fourth exemplary embodiment of the present inventiondemonstrating the tunnel effect-type magnetic sensor according to thepresent invention and the magnetic read head provided therewith. FIG. 5Ais a perspective view showing the tunnel effect-type magnetic sensor andthe magnetic read head provided therewith. FIG. 5B is a sectional viewshowing the tunnel effect-type magnetic sensor and the magnetic readhead provided therewith.

There is shown a substrate 101. On the substrate 101 are preferablysequentially formed: a lower magnetic shield 102; a metal layer 103 ofCu, Ta, or Ru; a ferromagnetic layer 501; a non-magnetic insulatinglayer 502; a soft magnetic free layer 503; a non-magnetic insulatinglayer 504; a ferromagnetic pinned layer 505; and an antiferromagneticlayer 506. The upper portion is connected to an upper magnetic shield110, with a metal layer 108 of Cu, Ta, or Ru interposed between them.The magnetic sensor, which consists of the soft magnetic free layer 503,the non-magnetic insulating layer 504, and the ferromagnetic pinnedlayer 505, has a front side which is connected to a flux guide 109 ofsoft magnetic material so that the leakage flux from the magneticrecording medium (not shown) is efficiently introduced into the magneticsensor 112.

Additionally, the tunnel effect-type magnetic head is preferablyconstructed such that the laminate film comprising layers 103 through108 is surrounded by an insulating layer 111 for electrical insulationbecause current has to flow from the lower magnetic shield 102 to theupper magnetic shield 110 only through the magnetic sensor 112. Thelower magnetic shield 102, the upper magnetic shield 110, and the softmagnetic free layer 503 are connected respectively to electrodes 114,113, and 507 for voltage application.

The ferromagnetic pinned layer 105 and the soft magnetic free layer 107are magnetized (in the absence of a magnetic field from the magneticrecording medium) such that their directions of magnetization (withintheir plane) mutually cross at approximately right angles. When amagnetic field (H) is applied from the magnetic recording medium to thesoft magnetic free layer 107 through the flux guide 109, the directionof magnetization within the plane of the soft magnetic free layer 107rotates, and the tunnel magnetic resistance between the soft magneticfree layer 503 and the ferromagnetic pinned layer 105 changes inproportion to the angle of rotation.

A detailed description will now be made of exemplary materials anddimensions for each layer. The antiferromagnetic layer 506 is composedof PtMn (12 nm thick). The ferromagnetic pinned layer 505 is formed fromCoFe alloy (3 nm thick). The CoFe alloy is not specifically restrictedin composition; it contains 90 atom % of Co. The non-magnetic insulatinglayer 504 is formed from SrTiO₃ (1 nm thick).

The soft magnetic free layer 503 is preferably a laminate comprised oflayers of NiFe (3 nm thick) and CoFe (1 nm thick). The CoFe alloy is notspecifically restricted in composition; in this embodiment, it iscomposed of Co (90 atom %) and Fe (10 atom %) for appropriate softmagnetic properties. Likewise, the NiFe alloy is not specificallyrestricted in composition; in this embodiment it is composed of Ni (81atom %) and Fe (19 atom %) This composition is called permalloycomposition.

The non-magnetic insulating layer 502 is formed from Al oxide(approximately 2 nm thick). The ferromagnetic layer 501, which is formedon the electrode metal layer 103, is composed of a 2-nm thick film ofα-Fe₂O₃ and a 10-nm thick film of Fe₃O₄ which is a half-metal magneticmaterial having a Curie temperature much higher than room temperature.The metal layers 103 and 108 are 14 nm thick and 12 nm thick,respectively, so that the soft magnetic free layer 503 is positioned atan approximately mid-point between the lower magnetic shield 102 and theupper magnetic shield 110. Thus the distance between the lower magneticshield 102 and the upper magnetic shield 110 is approximately 60 nm,which provides a linear resolution sufficient for a magnetic recordingapparatus for very high recording density (0.155 GB/mm² or 100GB/inch²).

The element composed of the layers between the lower electrode 103 andthe upper electrode 108 measures 0.3 by 0.3 μm. The forward end of theflux guide 109 measures 0.15 μm wide, 10 nm thick, and 50 nm long. Sincethe width of the forward end of the flux guide 109 determines theresolution (in the track direction) of the magnetic recording apparatus,the above-mentioned size is small enough for a magnetic recordingapparatus for very high recording density (0.155 GB/mm² or 100GB/inch²).

The operation of the device will now be detailed. In this embodiment,the current to detect the tunnel magnetoresistive effect is produced bythe bias voltage Vs applied across the electrodes 507 and 113, with theelectrode 507 being the reference. The electrode 114 is negativelybiased with reference to the electrode 507, so that downwardly spinpolarized tunnel electrons are injected into the soft magnetic freelayer 503 from the half-metal ferromagnetic layer 501. Thus the densityof the downward spin electrons increases in CoFe constituting the softmagnetic free layer 503, thereby enhancing the magnetoresistive effect.

FIG. 6 shows the dependence of the MR ratio of the tunnel effect-typemagnetoresistive head (constructed as shown in FIG. 5) on the biasvoltage Vs at room temperature (25° C.). It can be noted from FIG. 6that the MR ratio reaches a maximum when Vs is +0.5 V and decreasessteeply as Vs approaches 0 V. The maximum value of the MR ratio isapproximately 60%. This value is greater than that in the secondexemplary embodiment in which the CoFe alloy is used for both the softmagnetic free layer and the ferromagnetic pinned layer. The dependenceof MR ratio on bias voltage does not substantially vary in thetemperature range from 0° C. to 60° C. at which the magnetic recordingapparatus is used. When the magnetic field applied is zero, the electricresistance between the electrodes 507 and 113 is approximately 70 Ω,which is adequate for the magnetic read head.

Other materials to be used for the ferromagnetic layer 501 may includeCrO₂ and CuMnAl₂ as in the first exemplary embodiment. In the case whereCrO₂ is used, the above-mentioned orientation-controlling film may bemade of TiO₂, and the antiferromagnetic film is made of NiO. In the casewhere CuMnAl₂ is used, the orientation-controlling film is notnecessary, and the lower electrode layer 103 is preferably formed fromTa and CuMnAl₂ immediately thereon. Other materials for the non-magneticinsulating layer 504 may include Ta₂O₅ and MgO. Other materials for thenon-magnetic insulating layer 502 may include SrTiO₃, Ta₂O₅ and MgO.

The device depicted according to this embodiment has a flux guide 109;however, this structure may be modified such that the element composedof layers between the metal layer 103 to the metal layer 108 is exposedtoward that side of the magnetic sensor which faces the recordingmedium.

FIG. 7 shows an example of a magnetic recording-reproducing head whichis made up of the tunnel magnetoresistive magnetic read head (describedin any of the above embodiments) and an induction-type magneticrecording head formed thereon. The device shown in FIG. 7 is an examplein which the tunnel magnetoresistive magnetic read head shown in FIG. 1)is used. Similar magnetic recording-reproducing heads may be constructedsimply by replacing the tunnel magnetoresistive magnetic read head fromother embodiments.

In FIG. 7, there is shown a substrate 101. On the substrate 101 isformed the tunnel magnetoresistive magnetic read head shown in FIG. 1.On this read head are preferably sequentially formed a non-magneticinsulating layer 706, a lower magnetic core 704, and an upper magneticcore 701 which communicates with the lower magnetic core through a backcontact 702. Around the back contact is formed a coil 703 which inducesa magnetic flux in the magnetic core. The above-mentioned magneticrecording-reproducing head is installed in the proximity of the magneticrecording medium 705 to be magnetized in the direction of plane, forinformation recording and reproduction.

FIG. 8 shows an example of a magnetic recording-reproducing head whichis made up of the tunnel magnetoresistive magnetic read head describedin any of the above embodiments and a vertical magnetic recording headof single-magnetic pole type formed thereon. The device shown in FIG. 8is a particular example in which the tunnel magnetoresistive magneticread head shown in FIG. 1 is used. Similar magneticrecording-reproducing heads may be constructed simply by replacing thetunnel magnetoresistive magnetic read head from other embodiments.

In FIG. 8, there is shown a substrate 101. On the substrate 101 isformed the tunnel magnetoresistive magnetic read head shown in FIG. 1.On this read head are preferably sequentially formed a non-magneticinsulating layer 807, a lower magnetic core 804, and an upper magneticcore 801 of single magnetic pole type which communicates with the lowermagnetic core through a back contact 802. Around the back contact isformed a coil 903 which induces a magnetic flux in the magnetic core.The above-mentioned magnetic recording-reproducing head is installed inthe proximity of the vertical magnetic recording medium for informationrecording and reproduction. This magnetic recording medium comprises avertical magnetic recording layer 805 (to be magnetized in the verticaldirection with respect to the plane of the recording medium) and a softmagnetic backing layer 806.

FIG. 9 shows a magnetic recording-reproducing apparatus on which aremounted a slider 901 and a recording disc 902. The slider 901 ispreferably provided with any one of the magnetic read heads describedabove and a magnetic recording head. The recording disc 902 is mountedon an axis 904 connected to a spindle motor (not shown) fixed to thebase 903. The recording disc 902 is turned by the spindle, so that itmoves relative to the slider 901. The slider 901 is fixed to thesuspension 905, which in turn is attached to the arm 906. The arm 906 isturned around the axis 904 by the moving mechanism 907, so that theslider 901 is moved for tracking in the radial direction of therecording disc 902. The interface 908 attached to the base 903 has theconnector 909, to which is connected a cable for power supply (to drivethe apparatus) and information input and output (including commands tothe apparatus and information to be recorded and information which hasbeen read).

An exemplary version of the above-mentioned magneticrecording-reproducing apparatus provided with the tunnelmagnetoresistive magnetic head having improved dependence on biasvoltage was examined for output. The measured output was compared withthat of the conventional tunnel magnetoresistive magnetic head. Theresults are shown in FIG. 10.

The curve (b) in FIG. 10 shows the dependence of the signal-to-noiseratio on the bias voltage in the case of the tunnel magnetoresistivemagnetic head provided with the conventional tunnel magnetoresistivesensor which has the dependence of MR ratio on the bias voltage as shownin FIG. 11. It is noted that the S/N ratio reaches a maximum(approximately 25 dB) at Vs=−0.3 V and steeply decreases as the absolutevalue of Vs increases. The curve (a) in FIG. 10 shows the dependence ofthe signal-to-noise ratio on the bias voltage in the case of the tunnelmagnetoresistive magnetic head provided with the conventional tunnelmagnetoresistive sensor which has the dependence of MR ratio on the biasvoltage as shown in FIG. 3A which is identical with that shown in FIG.11 in which the maximum value of MR ratio is 30%. It is noted that theS/N ratio increases as the absolute value of Vs increases and reaches amaximum (34 dB) at Vs=−0.8 V.

The S/N ratio at Vs=−0.5 V (which is an operating voltage for a typicalmagnetic read head) is 9 dB greater in curve (a) than the S/N ratioshown by the curve (b) in FIG. 10. This occurs because the dependence ofMR ratio on the bias voltage is at a maximum at Vs=−0.5 V, which issuitable to drive the magnetic read head. In the cases shown in FIGS.2B, 3B, and 6, in which the maximum value of MR ratio is larger thanthat in FIG. 3A, the S/N ratio increases to a greater extent. Asmentioned above, the tunnel magnetoresistive sensor of the presentinvention, which is improved in the dependence of MR ratio on the biasvoltage, can be used to provide a tunnel magnetoresistive head having anextremely high sensitivity which is suitable for the magnetic recordingapparatus for extremely high recording density (e.g., higher than 0.155GB/mm² or 100 GB/inch²)

Nothing in the above description is meant to limit the present inventionto any specific materials, geometry, or orientation of elements. Manypart/orientation substitutions are contemplated within the scope of thepresent invention and will be apparent to those skilled in the art. Theembodiments described herein were presented by way of example only andshould not be used to limit the scope of the invention.

Although the invention has been described in terms of particularembodiments in an application, one of ordinary skill in the art, inlight of the teachings herein, can generate additional embodiments andmodifications without departing from the spirit of, or exceeding thescope of, the claimed invention. Accordingly, it is understood that thedrawings and the descriptions herein are proffered by way of exampleonly to facilitate comprehension of the invention and should not beconstrued to limit the scope thereof.

What is claimed is:
 1. A magnetic sensor, comprising: a soft magnetic layer; a ferromagnetic layer; a non-magnetic layer interposed between the soft magnetic layer and the ferromagnetic layer such that the magnetization of said ferromagnetic layer is fixed with respect to a magnetic field to be detected; and a magnetoresistive film which changes in magnetoresistance accordingly as the magnetization of said soft magnetic layer rotates in response to an external magnetic field, thereby changing the relative angle with the magnetization of said ferromagnetic layer, wherein the magnetoresistance of the magnetoresistive film changes upon application of a detecting current across said soft magnetic layer and said ferromagnetic layer through said non-magnetic layer, with a peak of the absolute value of the ratio of change in magnetoresistance of said magnetoresistive film being greater than 20% and occurring at a temperature in the range from 0° C. to 60° C. and with a bias voltage applied across said ferromagnetic layer and said soft magnetic layer being in ranges of +0.2 to +0.8 V and −0.8 to −0.2 V.
 2. The magnetic sensor as defined in claim 1, wherein the ferromagnetic layer contains Fe₃O₄.
 3. The magnetic sensor as defined in claim 2, wherein the non-magnetic layer is comprised of a material selected from the group consisting of at least one oxide of Sr, at least one oxide of Ti, at least one oxide of Ta, and a combination thereof.
 4. The magnetic sensor as defined in claim 2, wherein the soft magnetic layer is comprised of a film of an alloy containing Co and Fe or a laminate film formed by sequentially depositing an alloy containing Co and Fe and an alloy containing Ni and Fe.
 5. The magnetic sensor as defined in claim 1, wherein the ferromagnetic layer is comprised of a material selected from the group consisting of at least one oxide of Cr, at least one oxide of Mn, a compound containing Cr, a compound containing Mn, and a combination thereof.
 6. The magnetic sensor as defined in claim 5, wherein the non-magnetic layer is comprised of a material selected from the group consisting of at least one oxide of Sr, at least one oxide of Ti, at least one oxide of Ta, and a combination thereof.
 7. The magnetic sensor as defined in claim 5, wherein the soft magnetic layer is comprised of a film of an alloy containing Co and Fe or a laminate film formed by sequentially depositing an alloy containing Co and Fe and an alloy containing Ni and Fe.
 8. The magnetic sensor as defined in claim 1, wherein the non-magnetic layer is comprised of a material selected from the group consisting of at least one oxide of Sr, at least one oxide of Ti, at least one oxide of Ta, and a combination thereof.
 9. The magnetic sensor as defined in claim 1, wherein the soft magnetic layer is comprised of a film of an alloy containing Co and Fe or a laminate film formed by sequentially depositing an alloy containing Co and Fe and an alloy containing Ni and Fe.
 10. A magnetic sensor according to claim 1, wherein said peak includes a maximum value.
 11. A magnetic sensor, comprising: a half-metal magnetic layer; an alloy layer containing Co and Fe; a non-magnetic insulating layer comprised of at least one oxide of Sr, Ti, and Ta, which is interposed between the magnetic layer and the alloy layer such that the magnetization of said half-metal magnetic layer is fixed with respect to a magnetic field to be detected; and a magnetoresistive film which changes in magnetoresistance as the magnetization of said alloy layer rotates in response to an external magnetic field, thereby changing the relative angle with the magnetization of said half-metal magnetic layer, wherein the magnetoresistance of said magnetoresistive film changes upon application of a tunnel current across said half-metal magnetic layer and said alloy layer through said non-magnetic layer, with a peak of the absolute value of the ratio of change in magnetoresistance of said magnetoresistive film being greater than 20% and occurring at a temperature range of 0-60° C. and with a bias voltage applied across said ferromagnetic layer and said soft magnetic layer in ranges of −0.8 to −0.2 V and 0.2-0.8 V.
 12. The magnetic sensor as defined in claim 11, wherein the half-metal magnetic layer comprises at least one material selected from the group consisting of CrO₂, CrMnAl₂, and Fe₃O₄.
 13. A magnetic sensor according to claim 11, wherein said peak includes a maximum value.
 14. A magnetic head, comprising: a magnetic sensor comprised of (a) a soft magnetic layer, (b) a ferromagnetic layer, (c) a non-magnetic layer interposed between the soft magnetic layer and the ferromagnetic layer such that the magnetization of said ferromagnetic layer is fixed with respect to a magnetic field to be detected, and (d) a magnetoresistive film which changes in magnetoresistance accordingly as the magnetization of said soft magnetic layer rotates in response to an external magnetic field, thereby changing the relative angle with the magnetization of said ferromagnetic layer, with a peak of the absolute value of the ratio of change in magnetoresistance of said magnetoresistive film being greater than 20% and occurring at a temperature range of 0-60° C. and with a bias voltage applied across said ferromagnetic layer and said soft magnetic layer in ranges of −0.8 to −0.2 V and 0.2-0.8 V; a pair of magnetic shields; and a metal layer interposed between said magnetic sensor and said magnetic shields to electrically connect said magnetic sensor to said magnetic shields.
 15. The magnetic head as described in claim 14, wherein said sensor, said shields and said metal layer form a magnetic read head.
 16. The magnetic head as described in claim 14, further comprising: a vertical magnetic recording head of single-magnetic pole type.
 17. The magnetic head as described in claim 14, further comprising: an induction-type magnetic recording head.
 18. A magnetic head according to claim 14, wherein said peak includes a maximum value.
 19. A magnetic storage apparatus, comprising: a recording medium; a magnetic sensor comprised of (a) a soft magnetic layer, (b) a ferromagnetic layer, (c) a non-magnetic layer interposed between the soft magnetic layer and the ferromagnetic layer such that the magnetization of said ferromagnetic layer is fixed with respect to a magnetic field to be detected, and (d) a magnetoresistive film which changes in magnetoresistance accordingly as the magnetization of said soft magnetic layer rotates in response to an external magnetic field, thereby changing the relative angle with the magnetization of said ferromagnetic layer, with a peak of the absolute value of the ratio of change in magnetoresistance of said magnetoresistive film being greater than 20% and occurring at a temperature range of 0-60° C. and with a bias voltage applied across said ferromagnetic layer and said soft magnetic layer in ranges of −0.8 to −0.2 V and 0.2-0.8 V; a pair of magnetic shields; and a metal layer interposed between said magnetic sensor and said magnetic shields to electrically connect said magnetic sensor to said magnetic shields; wherein said sensor, said magnetic shields, and said metal layer form a magnetic read head used to read information stored on the recording medium.
 20. The magnetic storage apparatus of claim 19, further including a magnetic recording head.
 21. The magnetic storage apparatus of claim 19, wherein said soft magnetic layer, said ferromagnetic layer, and said non-magnetic layer are exposed on a surface adjacent to said recording medium.
 22. A magnetic storage apparatus according to claim 19, wherein said peak includes a maximum value. 